Contractual Maturity By Number Of Years Until Maturity for Fixed Maturity Securities With Gross Unrealized Loss (Detail) (Fixed maturities, USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	$ 4,072	$ 10,782
Percent of Total Gross Unrealized Loss	100.00%
Fair Value Amount	313,550	305,121
Percent of Total Fair Value	100.00%
Due in one year or less
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	102
Percent of Total Gross Unrealized Loss	3.00%
Fair Value Amount	12,586
Percent of Total Fair Value	4.00%
Due after one year through five years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	938
Percent of Total Gross Unrealized Loss	23.00%
Fair Value Amount	183,891
Percent of Total Fair Value	58.00%
Due after five years through ten years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	694
Percent of Total Gross Unrealized Loss	17.00%
Fair Value Amount	52,004
Percent of Total Fair Value	17.00%
Due After Ten Years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	201
Percent of Total Gross Unrealized Loss	5.00%
Fair Value Amount	26,771
Percent of Total Fair Value	9.00%
Mortgage- and asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	2,137
Percent of Total Gross Unrealized Loss	52.00%
Fair Value Amount	$ 38,298
Percent of Total Fair Value	12.00%